1. Field of the Invention
The present invention relates generally to measuring devices, and more particularly to a measuring device that measures characteristics such as fetal electrocardiogram, temperature and intra-uterine pressure to determine fetal health during intra-operative and postoperative periods.
2. Description of the Prior Art
Improvements in obstetrical ultrasound have stimulated continuous improvements in a doctor's ability to treat congenital anomalies. In the past twenty years it has become possible to treat a fetus with a congenital anomaly in a progressively interventional fashion. Fetal cardiac arrhythmia's can be treated pharmacologically, see "Treatment of Fetal Arrhythmias," Wladimiroff & Stewart, Br. J. Hosp. Med. (1985). Fetal anemia can be corrected by intra-uterine transfusion of blood, see "Intrauterine Transfusion of Fetus in Hemolytic Disease," Liley, A. W., Br. Med. J., 5365: 1107-1109 (1963). Additionally, some fetal conditions are amenable to percutaneous catheter drainage, see "Catheter Shunts for Fetal Hydronephrosis and Hydrocephalus," Manning, Harrison & Rodeck, N. Eng. J. Med., 315: 336-340 (1986). Finally, there are some highly selected life-threatening fetal anomalies that can only be treated by hysterotomy and open surgical repair of the fetal defect. For example, bilateral urinary tract obstructions, congenital diaphragmatic hernia, and some types of fetal tumors have all been treated by open surgical repair. For further information on fetal surgical procedures, see "Early Experience with Open Fetal Surgery For Congenital Hydromephrosis," Crombleholme, Harrison & Langer, J. Pediatr. Surg., 23: 1114-1121 (1988); "Correction of Congenital Diaphragmatic Hernia In-Utero. V. Initial Clinical Experience," Harrison et al., J. Pediatr. Surg., 25: 47-57 (1990); "Successful Repair In-Utero of a Fetal Diaphragmatic Hernia After Removal of Herniated Viscera from the Left Thorax," Harrison et al., N. Eng. J. Med., 322: 1582-1584 (1990); "Fetal Hydrops and Death from Sacrococcygeal Teratoma: Rational for Fetal Surgery," Langer, Harrison & Schmidt, Am. J. Obstet. Gynecol., 160: 1145-1150 (1989); and "Antenatal intervention for Congenital Cystic Adenomatoid Malformation," Harrison, Adzick & Jennings, Lancet, 336: 965-967 (1990).
As may be seen from the above articles, the need for an accurate device for monitoring fetal health is vital for increasing the success rate of the above mentioned surgical procedures. The monitoring of the fetus is critical to fetal health care management and is also an aid in the monitoring of the onset of parturition. Thus, there are two critical periods for monitoring a fetus, 1) during intraoperative and postoperative periods as well as 2) during the onset of parturition.
The current techniques for monitoring fetal health include the monitoring of the fetal electrocardiogram during intraoperative periods or the use of ultrasound for postoperative periods. In both situations, there are significant drawbacks to these techniques.
During the intraoperative period, pulse oximetry, percutaneously placed electrical leads, and sterile intraoperative ultrasound are utilized for determining fetal cardiac function. These devices are generally designed for an adult and thus the sensitivity of the device is incapable of distinguishing the electrocardiogram signal of the fetus from that of the mother. Another problem with this type of device is the inability to secure the electrocardiogram leads, even with sutures. Additionally, these devices were designed to operate in a dry environment while the environment of the fetus is a fluid based environment. Thus, there is a problem with the electrical leads shorting and potentially burning or electrically shocking the fetus. In order to avoid this possibility, current techniques require the removal of the leads when the fetus is returned to the uterus. Thus, these techniques do not allow for continuous monitoring when the fetus is returned to the uterus and the hysterotomy is closed, a critical period of time when the umbilical cord may be kinked or the fetus may be compromised by poor positioning. Finally, fetal electrocardiography, pulse oximetry, and intra-operative ultrasound are cumbersome and the electrocardiography and pulse oximetry equipment have been unreliable in the past.
During the intra-operative period, the monitoring of fetal temperature is very important in the management of the fetus and the prevention of intraoperative hypothermia. Currently there are no devices which provide both fetal electrocardiogram and temperature signals.
During the postoperative period, the fetus may be monitored by electromagnetic or acoustical signals and a doppler effect thereon. For example, U.S. Pat. No. 3,606,879 (Estes) discloses an ultrasonic apparatus which is used for monitoring fetal heartbeat by detecting the change in frequency, due to a doppler effect, of an ultrasonic wave which passes through the fetus. Additionally, uterine contractions and cervical dilations are measured by the change in transit times of each pulse of ultrasonic energy. This doppler signal is intermittent and unreliable because of fetal movement and positioning, especially in the situation of fetal distress. The data from fetal doppler can be difficult to interpret. For example, a signal dropping in magnitude could mean either that the fetus has lost cardiac function or that the fetus has changed position. The use of real time ultrasound may only be performed intermittently, i.e., is limited by the availability of operator time to only once or twice per day. Other techniques such as fetal electrocardiogram (ECG) recordings across the maternal abdomen and fetal phonocardiography are ineffective with respect to fetus' because of the small signal to noise ratio. The use of fetal scalp ECG is not possible since the fetus is within the uterus with intact amniotic membranes.
As mentioned earlier, the second period for measuring fetal characteristics is during the onset of premature labor or parturition, child birth.
Each year in the U.S., 5% of all infants are born prematurely at an enormous cost to the health care system. Premature births account for 85% of neonatal deaths. About 10% of pregnant women in the U.S. are at risk or premature labor. Accurate detection or prediction of the occurrence of premature labor would allow the patient to be appropriately treated to suppress labor, thereby improving the chances that delivery will occur closer to term. The closer the delivery is to term, the lower the mortality rate and the lower the cost post-delivery neonatal care.
Several methods have been employed or proposed for detection or prediction of premature labor. These include both natural and instrument-based means.
Symptomatic self-monitoring is a natural means whereby the mother is educated in the symptoms of uterine contractions or cervical dilatation and receives regular counseling from a nurse. This approach has the advantage that it is non-invasive and inexpensive, since it can be done at home. However, it requires significant discipline, is time consuming for the patient, and lacks uniform accuracy. Mammary stimulation, cervical distensibility, and fetal breathing movements encompass other natural means. However, these methods require that the patient visit a care provider. They are therefore expensive and inconvenient.
Intrauterine pressure (IUP) measurement devices are considered to be the most accurate means available for measuring frequency of occurrence, duration, and intensity of uterine contractions. This technique has frequently been used to validate the accuracy of other methods of monitoring uterine activity. In this method a transvaginal catheter is inserted into the uterus. Open lumen fluid-filled catheters may be used, but require regular flushing to keep the lumen free of cellular debris. Catheters have been constructed with a balloon tip to eliminate the need for regular flushing. Microballoon-tipped catheters provide poor accuracy. Larger balloons provide better accuracy but their presence leads to irritation and artifactual stimulation to both the uterus and fetus. In addition, their use is restricted to bed-ridden patients and there is a risk of infection. Catheters that employ a solid state pressure transducer at the tip or fiber optic technology have also been used. Use of these techniques is generally limited to bed-ridden patients due to the risk of infection. An implantable pressuretelemetry device has also been used (Smyth, 1960) for monitoring intrauterine pressure. This device has been introduced into the uterine cavity external to the membranes to measure IUP following induction of labor. The authors suggest its use to "extending obstetric research and treatment control." No reference is made to using this device as a tool for prediction or detection or premature labor.
With the exception of symptomatic self-monitoring, use of the above methods has been restricted to a care providers office. However, successful treatment of preterm labor depends on early diagnosis (Iam, et. al., 1990) and these methods do not provide the timely information needed to effect prompt intervention and arrest labor. Methods suitable for monitoring patients as they go about their daily activities present a significant advantage in early diagnosis of preterm labor.
The guard-ring tocodynamometer provides a non-invasive means for monitoring uterine activity and represents the current state-of-the-art for detecting premature labor in ambulatory patients. This device is placed on the maternal abdomen and held in place by an elastic belt. It employs a "guard-ring" to flatten the abdomen within an area over which pressure applied to a sensing diaphragm by the abdominal tissues is sensed. Pressure measurements taken at this flattened area are representative of intrauterine pressures. Some commercially available tocodynamometers are capable of transmitting data to a clinic or doctors office via telephone lines. Studies of the effectiveness of these devices have demonstrated variable results.
In an attempt to provide doctors with accurate information on the condition of their patient during labor, many devices have been designed to detect both the onset of labor and the condition of the mother during the birthing process. The determination of the onset of labor is even more important when fetal surgery has been performed since preterm labor is a substantial problem associated with fetal surgery.
An example of one method for detection of parturition is the use of temperature sensors to detect temperature changes in a mother. U.S. Pat. No. 4,651,137 (Zartman) discloses an intravaginal parturition alarm and method for its use. The device comprises an anchor, a temperature sensor affixed to the anchor, and an alarm. During the onset of parturition, the anchor is displaced from an anterior portion of the female's vagina and is expulsed to a posterior portion of the vagina. The temperature sensor detects the change in temperature between the two vaginal regions and activates the alarm. As is obvious, this method is highly invidious.
Aside from the use of the temperature change upon expulsion of an object from the reproductive tract as an indicator of parturition, others have attempted without success to show a reliable relationship between temperature phenomena and the onset of parturition and related events. Research reports may be summarized as describing a body temperature increase during the latter part of pregnancy, with a substantial drop during the last few days to a few hours before parturition. However, for a number of reasons, the efforts of workers in the field to develop a reliable relationship between temperature phenomena and the onset of parturition have failed.
In fact the prior art would actually lead one away from the use of temperature measurements as a reliable tool in the forecasting and identification of occurrences related to parturition. Researchers in the field generally reported failures in their attempts to use such measurements in forecasting and determining occurrences related to parturition, thus dissuading other researchers from further study. Additionally, with only one exception, no current textbooks on reproductive physiology have been found that comment on any temperature phenomenon related to parturition.
Detection of parturition in animals has been accomplished in various ways. For example, U.S. Pat. No. 4,707,685 (Carrier et al.) discloses a system for detection of parturition which in effect is a continuity circuit. When a cow enters parturition, a thin wire, disposed about the animals vulva, is broken and thus continuity in an electric circuit is terminated. This lack of continuity sets off an alarm. U.S. Pat. No. 4,936,316 (Jewett) discloses the monitoring of the swelling of an animals vulva.
While significant efforts are made to monitor the mother, the other participant in the berthing process, i.e., the fetus, is generally ignored as a source for information. One vital sign which is measured is the fetal heartbeat. Physicians generally monitor the fetal heartbeat by using a stethoscope to determine the fetal condition. This method of fetal heartbeat monitoring is severely limited due to the shortcomings in the ability of an individual to instantaneously analyze the information transmitted to him and to detect suitable characteristics of the fetal heartbeat pattern.
The importance of continuous fetal heart rate monitoring and the shortcomings of evaluation by stethoscope are discussed in "An Introduction to Fetal Heartrate Monitoring" by Edward H. Hon M.D., published by the Postgraduate Division, University of Southern California School of Medicine. This publication also discusses problems associated with the monitoring of fetal heart rate caused by interference associated with uterine contractions during labor.
There has been an emergence of fetal monitoring devices which are utilized to monitor the status of the fetus during parturition. For example, U.S. Pat. No. 4,537,197 (Hulka) discloses a fetal oxygen monitor which is attached to the fetus' scalp after the onset of parturition, i.e, after the fetus' head is accessible through the vagina. The fetal monitor comprises a fetal scalp cap; a three channel catheter; two fiber optic bundles connected to the cap, one for transmitting light and the other for receiving light; and a oxygen level analyzer attached to the distal ends of the fiber optic bundles.
U.S. Pat. No. 3,989,034 (Hojaiban) discloses an apparatus for determining the heart rate of a fetus during labor. The device comprises a means for receiving a measured fetal heart rate signal; a means for receiving a uterus pressure signal; and a means for determining an actual fetal heart rate based upon the uterine pressure and the measured fetal heart rate.
U.S. Pat. No. 4,951,680 (Kirk et al.) discloses an apparatus for monitoring a fetus during labor. The apparatus comprises a scalp electrode for repeatedly deriving signals representative of the P-R interval of the fetal heart and the period of the fetal heartbeat; and a microprocessor for determining fetal health based upon the change in the above two signals.
None of these devices provide information on both fetal electrocardiogram and fetal temperature. Fetal temperature is an essential criteria to measure for determining fetal distress syndrome, which may occur before or during parturition. When fetal distress syndrome occurs, the fetus' temperature begins to climb dramatically, and the mother's temperature similarly undergoes a marked temperature increase. It is important to administer suitable treatment to remedy the problem as soon as possible in order to reduce the risk of fetal mortality or injury. For further information, please see: Weisz, "The Temperature Phenomenon Before Parturition and Its Clinical Importance," J.A.V.M.A. 102: 123 (1943).
The automatic administration of drugs based upon medical characteristics of the patient are utilized in areas such as high blood pressure treatment, blood oxygen concentration problems, and the treatment of diabetes. For example, U.S. Pat. No. 4,003,379 (Ellinwood) discloses a medication dispenser which is inserted into a patient's body and will dispense upon particular conditions being present. The dispenser comprises at least one sensor, control circuitry, a power source, a dispensing means, and medication storage means. Sensors and logic control circuitry are provided within the dispenser for measuring the existence or absence of a particular condition such as high blood pressure. The sensors may include 1) blood pressure detecting devices; 2) electrical activity from the carotid sinus or aortic body; 3) possible electrical activity from the sympathetic outflow; and 4) electrocardiogram.
U.S. Pat. No. 4,543,955 (Schroeppel) discloses a medical implant which includes a sensor assembly disposed remotely from the implant; signal converting circuitry for converting the signals from the sensor to a coded signal, a transmitting means for transmitting the coded signal, and an activation device for receiving the coded signal and actuating the activation device based upon the coded signal. The parameters sensed by this system are body temperature, blood oxygen concentrations or blood potassium concentrations.
U.S. Pat. No. 4,596,575 (Rosenberg et al.) discloses an insulin dispenser. The device comprises an implant having a transducer, an electronic control unit, a piezoelectric pump and an insulin reservoir. In operation, an external controller provides an actuation signal to the transducer which in turn sends an actuation signal to the electronic control unit. The control unit actuates the piezoelectric pump which in turn forces insulin to be dispensed from the reservoir.
While the prior art has appreciated the importance of suitably administering treatment to the mother and fetus upon the occurrence of fetal stress syndrome, the prior art has failed to adequately provide a means for detecting the onset of fetal stress syndrome and automatically administering the required treatment.
Although current technology is available for comparing measurements expressed in quantitative form with quantitative tolerance limits and signaling when those limits are exceeded and activating a device for the administration of medication based upon this information, the evaluation of the fetal condition has, until now, often been a qualitative one beyond the capabilities of the known state of the art identified above. Additionally, the prior art does not provide any teachings for continuously monitoring a fetus before the onset of parturition. This monitoring would be vitally important in cases where fetal surgery has been performed.